A reciprocating saw machine is a hand-held power saw that includes a chuck for releasably engaging the saw blade and driving the saw blade in a reciprocating motion through a work piece. The reciprocating motion can be an orbital cutting action, a straight or linear cutting action, or an angled cutting action. The length or stroke of the reciprocating motion is typically about 1½ inches or less. Reciprocating saws are sometimes referred to as recip saws, jig saws, and power hack saws, and the term reciprocating saw is used herein without limitation to mean reciprocating saw machines, jigsaw machines, and portable power hack machines. Reciprocating saws are typically driven by electric motors (e.g., cord or cordless saws) or are pneumatically driven. Well known reciprocating saws are sold under the brand names “Sawzall™” by Milwaukee Electric Tool Corporation and “Tiger Saw™” by Porter-Cable Corporation.
A typical reciprocating saw blade includes a blade portion having a cutting edge defined by a plurality of teeth axially spaced relative to each other along one side of the blade, and a non-working edge formed on an opposite side of the blade relative to the cutting edge. A tang for releasably connecting the blade to the chuck of a reciprocating saw extends from an inner end of the blade. The term “recip blade” or “reciprocating saw blade” is used herein to mean a blade configured for use in a reciprocating saw.
As shown in FIG. 1A, a typical prior art recip blade exhibits a tooth form defining a tip 1, a rake face 2 located on one side of the tip, and a clearance surface 3 located on an opposite side of the tip relative to the rake face defining a clearance angle 4. The tooth form of FIG. 1A defines a single or primary clearance surface 3 that runs from the tip of the tooth to the respective gullet radius. In order to cut faster, some such prior art recip blades define relatively steep clearance angles, e.g., about 35° or greater. As a general matter, the steeper the clearance angle, the more sharply pointed is the tooth form, and the faster is the speed of cut. One drawback associated with such prior art recip blades is that the teeth defining such steep clearance angles are relatively weak, and thus prone to premature fracture, particularly when subjected to abusive cutting applications, such as in demolition where there are interrupted cuts of hard objects that are embedded within softer materials, like nail embedded wood, nail or screw embedded sheetrock, or plaster bonded to metal lath.
Prior art attempts to solve the problem of premature tooth fracture include using different set styles wherein multiple teeth are set to the same position to reinforce the teeth of like set position. Although helpful, this feature has not satisfactorily addressed the problem. Another attempt to solve the problem of premature tooth fracture involves providing the teeth with very low or shallow clearance angles in order to make the teeth wider and more robust. A typical such prior art recip blade is shown in FIG. 1B and exhibits a tooth form defining a tip 1, a rake face 2 located on one side of the tip, a primary clearance surface 3 defining a primary clearance angle 4, and a secondary clearance surface 5 defining a secondary clearance angle 6. As can be seen, the secondary clearance angle 6 is steeper than the primary clearance angle 4. A typical such prior art blade defines a primary clearance angle 4 of about 20° and a secondary clearance angle 6 of about 40°. Although these tooth forms are more robust in comparison to the tooth forms with relatively steep single clearance angles, such tooth forms tend to develop relatively large wear lands at the junction of the tip 1 and primary clearance surface 3 more quickly than otherwise desired for a given amount of vertical wear of the tooth. As a result, one of the drawbacks of this type of tooth form is that the teeth tend to cut more slowly and tend to have a shorter life than otherwise desired in applications where tooth breakage is not the dominant mode of failure.
Accordingly, it is an object of the present invention to overcome one or more of the above-described drawbacks and/or disadvantages of the prior art.